In general, an air conditioner is provided with an indoor unit and an outdoor unit, which are electrically connected such that electric signals can be transferred to each other. However, in case where a plurality of indoor units are connected in parallel to one outdoor unit or a refrigerant pipe is installed in a wall of a building and a plurality of indoor units are connected in parallel to the refrigerant pipe, it is usually difficult to electrically connect each of indoor units to outdoor units, number of which is less than the number of indoor units.
Accordingly, a communication technology for pipes is being currently introduced to allow electric signals to be transmitted and received using a refrigerant pipe, as a communication medium, which connects a plurality of indoor units to a less number of outdoor units. For example, a communication device for pipes may be configured such that both ends of a gas-side refrigerant pipe (hereinafter, referred to as ‘gas pipe’ and both ends of a liquid-side refrigerant pipe (hereinafter, referred to as ‘liquid pipe’ are connected to indoor units and an outdoor unit, respectively, in an insulating manner, and signal lines which are connected to a control board of the indoor units and a control board of the outdoor unit are connected to the gas pipe and the liquid pipe. Consequently, the gas pipe and the liquid pipe can be used as communication media between the indoor units and the outdoor unit.
Here, the refrigerant pipe is provided with a core assembly which is installed to increase communication performance. The core assembly is typically configured such that a pair of cores each having a semicircular section is accommodated in core holders and coupled to surround a refrigerant pipe, and the core holders are coupled to signal terminals which electrically connect the refrigerant pipe to each control board to each other. The signal terminals are fixed or detachably coupled to the core holders in a contact state with the refrigerant pipe.
FIG. 1 is a perspective view illustrating one example of the related art core assembly, and FIG. 2 is a sectional view illustrating a state that the core assembly of FIG. 1 is coupled to a pipe. As illustrated in FIGS. 1 and 2, the related art core assembly 1 includes cores 2 each provided with a pipe insertion recess 2a at a center thereof and having a semicircular sectional shape, core holders 3 each having a semicircular sectional shape and provided with a pipe insertion recess 3a, in which the corresponding core 2 is inserted, signal terminals 4 closely coupled onto both ends of an inner circumferential surface of one of the core holders 3, respectively, and a terminal pin 3b provided on one end of an outer circumferential surface of the one of the core holder 3 and allowing a connection with a connector 5, which is connected to each control board (not illustrated) via signal lines 5a. 
In the core assembly 1 according to the related art, the core holders 3 are coupled to a gas pipe or a liquid pipe 6 (hereinafter, the gas pipe and the liquid pipe are collectively referred to as a refrigerant pipe and a reference numeral representatively denotes the liquid pipe) in a manner of surrounding the refrigerant pipe 6, such that the signal terminals 4 are closely adhered between an inner circumferential surface of each core holder 3 and an outer circumferential surface of the refrigerant pipe 6.
The terminal pin 3b is provided at the one of the core holder 3, and an inner end of the terminal pin 3b is connected to the signal terminal 4. An outer end of the terminal pin 3b is electrically connected to the connector 5 which is inserted into the terminal pin 3b for connection. Accordingly, the signal terminal 4 coupled to the core assembly 1 and the signal line 5a extending from each control board are electrically connected to each other, such that electric signals between the control boards are transferred to the refrigerant pipe 6.